'Barking' noise coming from engine... Cam/Fan belt?

I would like to ask a question about my Focus... I know this question probably wont make any sense because I really don't know how to explain/describe it properly.

Ok, so I have had my car since January 2007 and the car has been making the noise since I got it... I never thought anything of it because it didn't do it that often and was very quiet at first.

Well nowadays the noise comes more often, is louder and more frequent. The noise is coming from the engine obviously, the only way I can describe it without you hearing it yourself is it reminds me of the sound you hear whhen a dog is barking in the distance. The 'barking' noise sounds every 1 or 2 seconds (sounds like it's coming from a belt rubbing or something). The noise starts after about 10 mins of driving. It gets more faster and louder when the car gets hot or if I am stuck in a traffic jam in hot weather.

I opened the bonnet up earlier and can obviously hear the sound alot more clearer. As it's hot today the noise is every 1 second roughly and it sounds like it was coming from the visable belt (is that the fan belt? lol) on the left side of the engine.

Could this noise be coming from the fan or cam belt?

I'm sorry I haven't been able to describe it very well, but I am no mechanic and rely mainly on my dad or brother to help me.